The following relates generally to wireless communication, and more specifically to power management for devices (e.g., user equipment) that communicate wirelessly. Wireless communications systems are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., time, frequency, and power). Examples of such multiple-access systems include code-division multiple access (CDMA) systems, time-division multiple access (TDMA) systems, frequency-division multiple access (FDMA) systems, and orthogonal frequency-division multiple access (OFDMA) systems.
Generally, a wireless multiple-access communications system may include a number of base stations, each simultaneously supporting communication for multiple mobile devices. Base stations may communicate with mobile devices on downstream and upstream links. Each base station has a coverage range, which may be referred to as the coverage area of the cell. While power consumption by base stations may also be of concern, power consumption by wireless devices is of particular importance because such devices rely on power from one or more batteries.
Various approaches have been considered for minimizing power consumption by a device (e.g., cellular phone, tablet, etc.) of a wireless network. For example, this may be achieved by reducing an amount of time the device spends in an idle listening process and/or by intelligently adapting power mode states of the device (e.g., awake mode and sleep mode). Adapting power mode states may be particularly applicable to wireless local area networks (WLAN) which operate in a non-synchronized manner. The non-synchronized manner results in connected stations having to listen for downlink packets from the access point (AP) that are intended for the device. Thus, there may be a tradeoff between power saving and performance because the device is not listening and is not able to receive data while asleep.
WLAN systems, such as those employing the 802.11 family of standards (e.g., WiFi), may use channel sense multiple access (CSMA), in which devices or stations (STA) sense channel conditions prior to accessing the channel. In WLAN systems, access points (AP) may be communicating with several or many other STAs concurrently, and therefore data transfers may be interrupted by periods where the AP is serving other STAs. A baseline power-saving algorithm may keep the STA awake for a fixed period of time after the last received/transmitted frame. However, a long fixed period will sacrifice power savings for performance, while a short fixed period will save power but sacrifice performance.
One approach to solve this problem is to progressively enter and exit the sleep mode by sending null-data frames (with PM bit toggled). By frequently entering the low-power sleep mode, power consumption may be reduced. However, this approach suffers from drawbacks including power consumption for transmission of the null-data frames, which may be particularly high for multiple retries, for example, as a result of congestion on a channel.
Another approach is to use a packet arrival rate to adjust the period of time that the device remains in the awake mode after the last received/transmitted frame. The packet arrival rate, determined when the device is in the awake mode, is used to guide the determination of the period. However, this approach suffers from a drawback that the packet arrival rate determination may be in error, for example, due to channel congestion.